Modeling and implementation of sigma-delta modulation controller for DC/AC inverter

A sigma-delta modulation controlled DC/AC inverter is proposed. Modeling and analysis of sigma-delta modulation (SDM) controller are explored. The pulse width of the SDM formed by cycle-by-cycle integration loop is clearly described. System stability is studied by root-locus and Bode plot techniques. An approach to reducing the THD is conducted by Fourier analysis. A prototype of 1 kVA SDM controlled DC/AC inverter is designed and examined. Simulation and experiment are close to the theoretical predictions. The proposed inverter can provide high efficiency up to 90% under the rated power and still keep the total harmonic distortion (THD) without EMI filter within 2%.

I. Introduction

Realization of conventional DC/AC inverter is usually conducted by analog power amplification or by hard-switching of PWM inversion technologies. For the sake of reducing power dissipation in linear operation as well as large volume and heavy weight, the approach for power inversion by analog amplification is quite few employed nowadays. For achieving high efficiency, the pulse -width modulation (PWM) technique is widely used for DC/AC power inversion in particular for the uninterrupted power supply (UPS) [1] The general PWM control strategy for power inversion is always realized by comparing the modulating signal with the reference triangular train. The merit of the approach is to reduce harmonics and easy filter design at fixed frequency operation. However, it is difficult to have high stability and low harmonic by the PWM DC/AC inversion due to open -loop control strategy.